Propeller shroud



Dec. 6, 1960 D. A. FORTUNE PROPELLER SHROUD Filed Oct. 27, 1958 DONALD A. FORTUNE INVENT'OR HUEBNER 8 WORREL 44 TTORNEKS' BWM United States ice PROPELLER srmoun Donald A. Fortune, 1284 Wilson Ave., Fresno, Calif.

Filed Oct. 27, 1958, Ser. No. 769,690

' SCIaims. c1.1'1s--1s 4 The present invention relates to a propeller shroud and more particularly to an envelope for reducing the efficiency of a propeller, as for example in reducing the mini-' mum operable speed of a boat to less than it otherwise can attain. g

The sport of motorboating. generally involves two types of activities which usually cannot be achieved with a single boat. Racing, speedboating, and water skiing require high speed operation necessitating ample power, an efficient propeller and adequate propeller speed. Conversely, trolling requires very low operating speeds. Prior to the present invention, it was found that in the absence of expensive transmissions, speedboats could not reduce their operating speeds sufiiciently to suit them for, trolling purposes. As a. result, the owners of speedboats who wished to troll either provided their boats with auxiliary trolling motors, or more frequently, utilized entirely separate boats for the purpose. L

An object of the present invention is to provide an attachment whereby speedboats can readily be adapted for trolling. V

Another object is to provide an efiiciency reducing shroud for a propeller.

Another object is to cover the tips or outer end portions of the blades of a propeller so as to reduce the resistance to rotation and the effectiveness of the propeller in a fluid medium.

Another object is to provide an elastic annular shroud or envelope adapted to circumscribe a propeller in releasably fittedrel-ation on the blades of the propeller. 7

Another object is to enable the use of the same motor on a boat for high speed and low speed operations.

Another object is to enable a motorboat to be used for water skiing and fishing without changing the motor or propeller thereof.

Other objects are to provide a cover or envelope of the type described which is simple and economical to .construct and use, dependable in action, durable, adapted for use with motors and propellers of various sizes and types, and one which is easy to attach and remove.

These, together with other objects and advantages, will become more fully apparent upon reference to the following description.

In thedrawing: V

. Fig. l is a fragmentary side elevation of a motorboat and of a motor mounted on the stern of theboat.

Fig. 2 is a somewhat enlarged rear elevation of th propeller of the motor of Fig. l and of the shroud of the present invention applied to the propeller.

Fig. 3 is a diametric section taken on line 3-3 of Fig. 2.

Referring more particularly to the drawing, a' boat is partially shown in Fig. l and indicated by the numeral). A motor support bracket 11 is mounted on the stem 12 of the boat, and an outboard motor 14 provides a hanging bracket 15 supported on the bracket 11 and is pivotally movable about a substantially horizontal axis defined by a pivot pin 16. The motor provides a housing 17 which is front andrear walls intermediate the blades.

2,962,999 Patented Dec. 6, 1960 2 upright when the motor is in operating position and a propeller 18 connected to a propeller shaft 19, all as is well-known. While the instant invention is illustrated in connection with the outboard motor shown, it will be apparent that it is as suitably employed with any other motor desired.

The propeller 18, as is best illustrated in Figs. 2 and 3, includes a hub 25 rigidly connected to the propeller shaft 19 and a plurality of blades 26 rigidly outwardly extended from the hub in equally angularly spaced relation. The blades have inner end portions or roots 27 and outer end portions or tips 28. Further, the blades provide aft surfaces 30 and forward surfaces 31. A propeller nut 32 is connectedto the propeller shaft for holding the hub in fixed position on the shaft. The motor 14 is adapted for pivotal movement between the upright operating position of Fig. 1 wherein the propeller blades 26 are immersed in water, and a nonoperating position with the housing 17 substantially horizontally outwardly extended from the stem 12 of the boat 10. V p 7 The subject invention is embodied in an annular elastic, flexible shroud or envelope 40, preferably of sheet rubber, or elastic flexible sheet plastic, and provides opposed rear and front walls 41 and 42, respectively, integrally interconnected and defining therewithin'an annular concavity 43. The frontand rear walls have inner annular edges 44 which cirurnscribe a centnal opening in the envelope. A plurality of snap fasteners 48 are mounted in the front and rear walls ofthe envelope in circumferentially spaced positions therearound cooperatively to interconnect the The desi'g nation of the walls as being front and rear only for descriptive convenience and is not intended to limit positioning of the envelope which will be seen to be reversib1e.

When the envelope 40 is relaxed, that is, not stretched, it is of approximately circular shape having aradius generally corresponding to, but slightly less than, the radial distance between the axis of the propeller 18'1and'the terininal edge of each of theblades 26 Operation The operation and use of the described embodiments of the subject invention is believed to be readily apparent and is briefly summarized at this point. e 8

When the boat 10 is used for towing water skiers, or for high speed pleasure operation, for example, the motor 14 is employed without the shroud 40 and is operated in the usual manner to propel the boat at high speeds through the water. 1

However, if it is desired to use the boat 10 for trolling for fish, it is necessary to motivate the boat ata very slow speed. Accordingly, the shroud 40 is stretched over the propeller 18 in circumscribing relation thereto and so that the blades 26 fit into the concavity 43. The front and rear walls 42 and 41 of the shroud are disposed generally against the front and rear surfaces 31 and 30, respectively, of the blades. Since the blades are longitudinally helical and since the shroud is tensioned between the blades, the walls of the shroud are not entirely flush against the blade surfaces. However, it is to be noted that the envelope only covers the outer end portions of the tips 28 of the blades and leaves exposed the inner end portions 27' as well as the propeller shaft 19 and nut 32.

Normally, as suggested above, the elasticity of the shroud 40 tensions it between the blades 26 so as to hold it dpendably in position. 'However, the snap fasteners 48 are provided for connecting the front and rear walls 42 and 41 of the shroud between the blades 26. B This holds the shroud walls closer to the blade surfaces and insures more dependable retention of the shroud on the propeller 18 during movement through the water.

Thus, for trolling, with the shroud 40 on the propeller 18, the motor 14 is operated in the normal manner to rotate the propeller in the water. Since the outer end portions 28 of the blades 26 are covered, their propelling effectiveness is negligible. The shroud actually reduces resistance to rotation of the'blades in the water and 3 5 in certain instances reduces fuel consumption. However, since the inner end portions 27 of the blades are still exposed, the propeller does have some propelling effect to motivate the boat through the water. The speed at which the boat is traveled is considerably reduced, ,It is to be noted that the size of the opening 46 is selected so as to expose the desired amount of the blades 26 to achieve the desired minimum speed of travel ofthe boat. It will be evident that the size of the shroud 40 and its central opening 46 must be related to the size of the propeller in calculating such desired minimum speed. I i

From the foregoing, it will be apparent that a simple and economical device has been provided whereby a motorboat can be quickly and easily modified to travel at speeds appreciably less than their previous minimums. Whether the boat is an outboard of the type illustrated or an inboard, the shroud of the present invention can quickly and easily be installed by stretching the same over the propeller blades. As stated, the normal tension of the shroud holds it in place on the propeller and the snaps 48 need not be utilized unless desired. However, if there are moments during which the propeller may be operated at relatively high speeds so that the centrifugal force has a tendency to throw the shroud from the blades, the snaps are advantageous. The shroud of the present invention has made it possible for the owners of speedboats to enjoy trolling without the requirement of an auxiliary motor or a second boat.

Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A shroud for reducing the efiiciency of a propeller having a plurality of radiallv extended blades, as for adapting a motorboat for trolling which otherwise has a minimum operating speed too great for the purpose, comprising an annular elastic envelope adapted for tensioning in circumscribing relation about the blades of such a propeller and including annular opposed walls having interconnected peripheral portions and providing aligned central openings adapted to accommodate flow of water therethrough when the envelope is applied to the propeller and such propeller is operating in water.

2. A shroud for reducing the efiiciency of the propeller of a motorboat which has a hub and a plurality of radially extended circumferentially spaced blades and a normal path of water motivation substantially axially of the propeller through the spaces between the blades comprising an annular elastic envelope adapted for tensioning in circumscribing relation about such blades in obstructing relation to the path of water motivation, said envelope including fore and aft walls having concentric aligned hub receiving o enings therein.

3. The combination of a propeller for a motor adapted for use in ropelling a boat throu h the water, which propeller provides a plurality of blades having outwardly extended end portions, and an annularelastic envelope circumseribing the propeller and providing a concavity receiving the outwardly extended end portions of the blades, the envelope conforming to portions of the blades and partially covering the blades for reducing the propelling efiiciency of the propeller in the water.

4. In combination with a motor having a propeller providing a plurality of blades radiating outwardly from a shaft and adapted for use on a boat for propelling the boat through the water atrelatively high speeds, the blades having inner and outer end portions and fore and aft surfaces, means for reducing the etficiency of the propeller in the water to enable motivation of the boat through the water at speeds substantially less than the minimum speed otherwise attainable with said motor and propeller comprising an annular elastic flexible envelope including a pair of opposed integrally interconnected annular side walls providing a concavity therewithin opening inwardly of the envelope toward a central opening thereof circumscribed by inner edges of the walls, the envelope being releasably stretched over the blades of the propeller in circumscribing relation therearound, with the fore and aft surfaces of the outer end portions of the blades being overlaid by the walls of the envelope, and with the inner portions of the blades being exposed within the central opening in the envelope whereby the efiiciency of the propeller is reduced by the envelope to reduce the minimum operable speed of the boat.

5. The combination of a propeller for a motor adapted for use in propelling a boat through the water, which propeller provides a plurality of blades having outwardly extended end portions, and an annular envelope of elastic sheet material tensioned about the blades of the propeller and providing a concavity receiving the outwardly extended end portions of the blades thereby partially covering the blades for reducing the propelling efiiciency of the propeller in the water.

6. The combination of a propeller for a motor adapted for use in propelling a boat through the water, which propeller provides a plurality of blades having outwardly extended end portions, an annular envelope circumscribing the propeller and providing a concavity receiving the outwardly extended end portions of the blades thereby partially covering the blades for reducing the propelling efficiency of the propeller in the water, the blades being in angularly spaced relation to each other, the envelope being elastic and stretched over and between adjacent blades, the envelope also including opposed side walls overlying opposite surfaces of the blades, and means provided on the side walls for interconnecting the same between adjacent blades.

7. The combination of claim 6 wherein said means are snap fasteners.

8. In combination with a motor having a propeller providing a plurality of blades radiating outwardly from a shaft and adapted for use on a boat for propelling the boat through the Water at relatively high speeds, the blades having inner and outer end portions and fore and aft surfaces, means for reducing the efiiciency of the propeller in the water to enable motivation of the boat through the water at speeds substantially less than the minimum speed otherwise attainable with said motor and propeller comprising an annular elastic flexible envelope including a pair of opposed integrally interconnected annular side walls providing a concavity therewithin opening inwardly of the envelope toward a central opening thereof circumscribed by inner edges of the walls, the envelope being releasably stretched over the blades of the propeller with the fore and aft surfaces of the blades being overlaid by the walls of the envelope whereby the efiiciency of the propeller is reduced by the envelope to reduce the minimum operable speed of the boat.

References Cited in the file of this patent UNITED STATES PATENTS 1,986,867 Walsh Jan. 8, 1935 2,396,340 Paulson Mar. 12, 1946 2,460;237 Palmer Ian. 25, 1949 

